In most large airplanes, it is standard for floor beams to run in a lateral direction, except in the wing box section where the floor beams run in a forward and aft direction. As a result, the floor beams over the wing box flex (i.e., expand and contract laterally) with movement of the wings. While this flexing may occur at any stage of the airplane's flight, it is most pronounced as the wings bounce up and down during taxiing, especially at high gross weights. With airplanes that carry fuel in their wings, the wings have an even lower resting position and the resulting wing bounce exerts even greater flexing to the floor beams than is found in airplanes not carrying fuel in this manner.
In cargo airplanes, loaded containers and pallets normally sit two abreast across the width of the airplane, each container or pallet being secured to the main cargo deck on the inside by centerline restraints and on the outboard side by vertical restraints and side locks. Current side locks have a plunger that is extendable to engage a receptacle in the container or the top of the outboard lip of the pallet. As a result, the plunger acts as a vertical restraint for pallets and as both a vertical and horizontal restraint for containers.
End locks are always placed forward and aft of pallets to provide the required horizontal restraint, since the side locks provide none. End locks are also placed forward and aft of most containers to provide horizontal restraint in addition to that provided by the side locks. However, with containers of significant length (e.g.,20 and 40 feet), it is not possible to use end locks at all. Consequently, the sole horizontal restraint for these large containers is that provided by the side locks.
In order for the cargo containers and pallets to be loaded, the distance from the centerline restraints to the outboard vertical restraints and side locks must be slightly greater than the width of the container or pallet. If not, there would not be the clearance required to move the cargo into position. Additionally, it is quite common for containers and pallets to be slightly undersized because the manufacturers do not closely follow the dimensional specifications set for the containers and pallets.
Consequently, the combination of a slight amount of clearance, an undersized container or pallet, and the outboard movement of the side lock due to flexing of the beam upon which it is mounted may lead to the plunger being pulled out of engagement with the container or pallet. When this occurs with a large container not capable of being end locked, the container becomes unrestrained, which can lead to catastrophic events.
As a result, there has been a long-felt need for an outboard side lock for restraining large containers over the wing box section of cargo airplanes that maintains contact with the container even during periods of extreme floor beam flexing. This invention is directed to satisfying this need.